1. Field of the Invention
The present invention relates to a display unit such as an organic EL display and its manufacturing method.
2. Description of the Related Art
In late years, displays having various display mechanisms have been known. Specially, a full-color organic EL display which utilizes organic light emitting (organic EL (electroluminescence)) phenomenon is noted in point of its wide visual field angle, its low driving voltage, and its high luminance. Based on these advantages, lately, trials to mount the organic EL display on compact information terminal devices for personal use typified by a mobile phone and a PDA (personal digital assistant) have been made.
In the development field of the organic EL display, in order to assure luminance of display images, technological establishment to enable improvement of emission efficiency (extraction efficiency) of lights for image display has been desired. In particular, regarding the organic EL display mounted on the compact information terminal devices for personal use, improvement of emission efficiency in the direction facing the organic EL display (hereinafter simply referred to as “facing direction”) is expected. In order to realize this request, many proposals have been already made.
As a method to improve emission efficiency, for example, a method in which a micro lens or a micro prism as an optical component for light focusing which utilizes light refraction phenomenon is introduced to the organic EL display, in order to focus the lights for image display generated in a light emitting source (organic EL device) in the facing direction can be cited.
As a concrete organic EL display using the micro lens, for example, a structure wherein an aggregation of small micro lenses (micro lens array) is arranged on point light emitting organic EL devices which are pattern-arranged has been proposed (for example, refer to Japanese Patent Application No. H09-171892 (Ps. 3–5, FIG. 3)). This micro lens array, for example, is formed by utilizing a molding technique which uses a metal mold corresponding to a form of the micro lens. However, in a conventional molding technique, a metal mold for molding is prepared separately, and a molding process using this metal mold is required. Therefore, a manufacturing process for the micro lens array becomes complicated, and its manufacturing cost becomes high. As a technique to form the micro lens array, in addition to the molding technique which uses a metal mold, for example, a technique wherein a lens material is cut and ground can be utilized. In this case, since a high processing technique is required in processing curved surface parts of the micro lens, manufacturing the micro lens array becomes difficult, and its manufacturing cost becomes high.
It is said that manufacturing a spherical micro lens is relatively easy. However, in the case of using this spherical micro lens, while lights generated in the central part of the organic EL device are appropriately refracted and emitted in the facing direction as desired, lights generated at ends of the organic EL device are in result largely refracted and emitted in the directions other than the facing direction, though desired not to be largely refracted and to be emitted in the facing direction. In addition, there have been restrictions in using the micro lens, for example, since sufficient refraction index cannot be obtained with the spherical micro lens, in order to assure refraction index, labor to make a low refraction index media (e.g. air) adjacent to the micro lens is required.
Meanwhile, as a concrete organic EL display using the micro prism, for example, a structure wherein an aggregation of small micro prisms whose size is extremely small compared to a light emitting area (micro prism array) is arranged on a whole face light emitting organic EL devices has been proposed (for example, refer to “Electrophospherescent Organic Light Emitting Devices” by S. R. Forrest et al., May 21–23 in 2002, Society for Information Display 2002 International Symposium (Boston, Mass., U.S.)). However, in the organic EL display mounting the whole face light emitting organic EL devices, though at the micro prism, many of the lights generated in the organic EL device is focused in the facing direction, some lights generated at the position corresponding to boundary parts between each micro prism are hard to be focused in the facing direction at the micro prism, so that loss of emission efficiency is caused. A technical example that the micro prism array is arranged on the whole face light emitting organic EL devices is also disclosed by, for example, Takahashi et al. (for example, refer to Japanese Unexamined Patent Application No. H09-73983 (P. 1, FIG. 1).
For the above reasons, in the conventional organic EL displays, it is difficult to say that emission efficiency is sufficient, in spite that the micro lens or the micro prism is used. In addition, in the case where the micro lens or the micro prism is utilized in order to improve emission efficiency, there is a problem that difficulty in manufacturing is caused.